1. Field
The present invention relates to czochralski apparatuses for growing crystals and purification methods of waste salts using the same, more particularly, to a czochralski apparatus for growing crystals comprising a fixation screw assembly for fixing salt crystals mounted on a bottom end of a pulling bar of the apparatus in order to prevent desorption of crystals caused by load thereof during a crystal growing process without requiring alternative seed crystals and, in addition, a method for purification of waste salts, which can isolate impurities from molten waste salts using a czochralski crystal growing process without alternative adsorption medium, does not generate secondary wastes and may continuously purify the waste salts.
2. Description of the Related Technology
Conventionally known electrolytic reduction processes for spent oxide nuclear fuel convert constitutional elements into metal ingredients in LiCl molten salt baths. For instance, all of fission products excluding alkali metal, alkali-earth metal and some of rare-earth elements, as well as uranium and plutonium are converted into metal ingredients.
Since high heat generating chlorides of cesium Cs and strontium Sr or other chlorides dissolved in the LiCl molten salt in an electrolytic reduction process have relatively high standard free energy of formation (commonly called Gibbs free energy, Gf) and reduction potential and cannot be substantially dissociated by electrolysis, chemical processes and/or electrolysis.
Accordingly, in order to reuse salts, use of specific media such as zeolite is taken into account to isolate Cs and/or Sr from the salts. Adsorption of Cs and/or Sr using zeolite has been reported by Pereira C, et al. (Mater Res Soc Proc. 1999, vol 556, pp 115-120) and Lexa D, et al. (Metallurgical and Materials Transactions B. 2001; 32B:429-435), which is now known as one of the most practical processes for treatment or reuse of molten waste salts generated during treatment of nuclear spent fuels.
However, such adsorption method has a restriction of amount of fission products to be adsorbed and exhibits large quantities of adsorption medium based wastes generated after adsorption step.
Czochralski process, one of crystal growing processes, is commonly available in industrial semiconductor applications to mostly produce single silicon crystals. An illustrative example of czochralski process for LiCl treatment was reported by Hinks et al. in Materials Research Bulletin, vol 9, pp 53-64, 1974, that removed Fe, Co, Ni, Ca and the like by a zone refining process and produced LiCl single crystals.
Therefore, there is still a requirement for developing an improved process that can produce multi-crystalline LiCl and remove CsCl and SrCl2 contained in LiCl generated during treatment of nuclear spent fuels.